Aircraft, and most especially helicopters, require regular inspection and maintenance by trained mechanics. In order to gain close access to surfaces, parts or areas higher than can be reached while standing upon the ground, it is necessary to use a ladder or work platform of adequate height.
When work must be performed in the field, on the flight-line or elsewhere where no dedicated stationary platform is available, the mechanic will use a portable platform or ladder. Most frequently a conventional hinged aluminum folding-ladder is used. Such ladders are light in weight, can be carried by a single person and placed adjacent to the helicopter as required. Such ladders, however, are not stable. They can be hazardous when used correctly and dangerous when used incorrectly or when a mechanic is struggling to lift a heavy part or tool.
Furthermore, a conventional folding ladder cannot be positioned relative to the curved body of a helicopter in a manner so that the mechanic is positioned in close proximity to the aircraft. Whether placed parallel to or at an angle to the body of a helicopter, the poor fit of the ladder to the aircraft compromises the ability of the mechanic to perform his work and creates a hazardous condition when he is forced into awkward or unstable positions.
Lightweight, portable ladders or platforms that are truly safe, stable and which may be positioned so as to provide the kind of uncompromised access a mechanic requires are not known in the art. One product that is on the market is called the Aircraft MRO Pylon Ladder manufactured by Lock-N-Climb LLC (http://locknclimb.com/pylon-ladder/). This is a light-weight cantilevered aluminum stepladder that may be used for aircraft maintenance, but which fails to provide a truly safe and stable platform. This ladder is a conventional stepladder to which shortened support rails have been attached at about the mid-point of the stepped rails. To partially compensate for the shortness of the support rails, angled extensions have been affixed to the top end of those rails. It is apparent that the support legs will not fold flat against the stepped legs, thus making the ladder excessively bulky when in its folded position. The support legs are, of necessity, braced and cross-braced such that they cannot straddle the cross-tubes of a helicopter's skid assembly and would be unusable in many applications. Furthermore, because the support legs of the Pylon Ladder do not extend beyond the bottom of the stepped legs when the ladder is in the folded position and do not make a more acute angle to the ground than do the stepped legs when the ladder is in its open, operational, position, the Pylon Ladder would be expected to provide less than optimal resistance to forward tipping.
Folding step ladders are required by regulatory standards to have a locking mechanism on each side of the ladder that will prevent the spreader arms from articulating when the ladder is in use. More specifically, the purpose of this locking mechanism is to ensure that the ladder does not fold up when a worker is standing on the ladder rungs. The most conventional form of a locking mechanism is defined by the well-known braces that extend between the stepped side of the ladder and the support side of the ladder. The braces typically have a first elongate arm that is pivotally attached to a rail of the stepped unit, a second elongate arm that is pivotally attached to the support unit, and one-way locking hinge mechanism interconnecting the two elongate arms. In use, as the support unit is articulated away from the stepped unit to move the ladder to its open position, the braces are locked by pushing down on the one-way hinge mechanism. Doing so causes the spreader arms to align end-to-end or causes them to move into a slightly over-centered configuration. While no actual locking occurs at the brace mechanism, there is a frictional jamming that occurs and which is sufficient to ensure that the ladder will not collapse when stood upon.
The conventional spreader arm locks just described generally meet regulatory safety requirements and prevent an open ladder from closing when stood upon. These locks, however, do not engage automatically, and they require that the user push down the lock to fully engage the locking hinge mechanism when the ladder is opened. Failure to perform this action negates this safety feature and the ladder can accidentally collapse when in use. Moreover, the spreader arms may be inadvertently moved away from the locked position when the ladder is jostled and jarred as it is moved from one position to another. This has the potential of causing a dangerous condition where the spreader arms collapse when a user climbs the steps.
Additionally, most folding ladders have a fixed length. There are many known types of extension ladders, and there are known examples of folding or step ladders that have the ability to be extended. For example, some manufacturers have combined the structures of conventional extension ladders with folding step ladder design. But since many ladder users require ladders of varying lengths (as evidenced by the popularity of conventional extension ladders), there is a need for folding ladders that are able to be of multiple lengths and which are safe for the users.